Showing papers on "Transpiration published in 2010"
TL;DR: In this paper, the authors provide a synthesis of past research on the role of soil moisture for the climate system, based both on modelling and observational studies, focusing on soil moisture-temperature and soil moistureprecipitation feedbacks, and their possible modifications with climate change.
3,402 citations
TL;DR: It is concluded that differences in rooting depth expressed among iso-morphic wheat sister lines explains superior adaptation to drought, and accumulation of stem carbohydrates and deep rooting may be two alternative strategies for adapting to drought stress, the latter being beneficial where water is available at depth.
Abstract: Dehydration avoidance through cooler canopy temperature (CT) has been shown to explain over 60% yield variation in a random progeny derived from a Seri/Babax cross. A near ‘isomorphic’ subset of Seri/Babax progeny and parents encompassing a restricted range of height and phenology were used for detailed characterisation of drought-adaptive trait expression under contrasting water regimes. Under drought, five of the six progeny out yielded the best parent Babax by up to 35%. The main physiological attributes associated with drought adaptation were increased root dry weight at depth, transpiration rate – evidenced by grain carbon isotope discrimination (Δ13C) – grain filling duration and decreased CT during grain filling. Furthermore, increased root mass at depth was associated with reduced levels of stem water soluble carbohydrates (WSC) when comparing genotypes. It is concluded that differences in rooting depth expressed among iso-morphic wheat sister lines explains superior adaptation to drought. These effects can be detected in season using remote sensing. In addition, the data suggest that accumulation of stem carbohydrates and deep rooting may be two alternative strategies for adapting to drought stress, the latter being beneficial where water is available at depth.
358 citations
TL;DR: The survival of, and recovery from, water stress in Callitris are accurately predicted by the physiology of the stem water-transport system, indicating xylem reiteration as the primary means of hydraulic repair.
Abstract: Summary • Motivated by the urgent need to understand how water stress-induced embolism limits the survival and recovery of plants during drought, the linkage between water-stress tolerance and xylem cavitation resistance was examined in one of the world’s most drought resistant conifer genera, Callitris. • Four species were subjected to drought treatments of )5, )8 and )10 MPa for a period of 3‐4 wk, after which plants were rewatered. Transpiration, basal growth and leaf water potential were monitored during and after drought. • Lethal water potential was correlated with the tension producing a 50% loss of stem hydraulic conductivity. The most resilient species suffered minimal embolism and recovered gas exchange within days of rewatering from )10 MPa, while the most sensitive species suffered major embolism and recovered very slowly. The rate of repair of water transport in the latter case was equal to the rate of basal area growth, indicating xylem reiteration as the primary means of hydraulic repair. • The survival of, and recovery from, water stress in Callitris are accurately predicted by the physiology of the stem water-transport system. As the only apparent means of xylem repair after embolism, basal area growth is a critical part of this equation.
291 citations
TL;DR: It is proposed that an individual leaf optimally and autonomously regulates stomatal opening on short-term (approx. 10-min time-scale) rather than on daily or longer time-scales, thereby making the approach useful for climate models.
286 citations
TL;DR: This article measured δD values of precipitation (δD_p), groundwater, xylem water, and leaf water to understand their impact on the D/H ratio of plant leaf wax nalkanes in an arid ecosystem.
266 citations
TL;DR: Drought-tolerant nitrogen fixation had the greatest benefit of all traits with a yield gain in more than 85% of the years at nearly all locations, and in those cases with no yield increase there was only a very small yield loss.
Abstract: A number of plant traits have been suggested to ameliorate the effects of water deficits on crop yield. A quantitative response across a range of years and location is needed because many traits that could be beneficial in dry years might also be detrimental in wet years. This analysis was undertaken using a robust simulation model of soybean (Glycine max (L.) Merr.] development and growth to quantify yield changes as a result of modification of five traits: rooting depth extension, rate of leaf area development, decreased stomata conductance at high soil water content, reduced maximum transpiration rate, and drought-tolerant nitrogen fixation. Simulations were done for 50 yr of weather data for 2655 grid locations of 30 km by 30 km size in the United States. Slow rate of rooting development was a neutral or negative trait in most locations. Slow leaf area development proved beneficial in less than half the years and in wetter years it resulted in yield losses. Water conservation both by early decrease in stomata conductance with soil drying and by reducing the maximum transpiration rate resulted in yield increases in many locations in 70% or more of the years. Both traits resulted in only small yield decreases in the wet years. Drought-tolerant nitrogen fixation had the greatest benefit of all traits with a yield gain in more than 85% of the years at nearly all locations, and in those cases with no yield increase there was only a very small yield loss.
226 citations
TL;DR: In this article, the use of SDV records for irrigation scheduling is discussed, which is a clear advantage over conventional indicators such as stem water potential (Ψstem) and stem growth rate (SGR).
217 citations
TL;DR: How environmental cues might modulate this pathway such that gas exchange is optimized to suit the prevailing environmental conditions is discussed.
216 citations
TL;DR: In this paper, a study of coffee agroforestry systems in Southern Mexico (Chiapas, Mexico) was conducted to examine the ability of shade trees to maintain water availability for the coffee crop in a shade agroecosystem.
212 citations
01 Jan 2010
TL;DR: In this article, the authors present current knowledge and relevant results that aim to improve water use efficiency (WUE) in grapevines by biotechnology and genetic engineering, and modelled the expected benefits of these manipulations on WUE under water stress conditions.
Abstract: Improving water use efficiency (WUE) in grapevines is essential for vineyard sustainability under the increasing aridity induced by global climate change. WUE reflects the ratio between the carbon assimilated by photosynthesis and the water lost in transpiration. Maintaining stomata partially closed by regulated deficit irrigation or partial root drying represents an opportunity to increase WUE, although at the expense of decreased photosynthesis and, potentially, decreased yield. It would be even better to achieve increases in WUE by improving photosynthesis without increasing water loses. Although this is not yet possible, it could potentially be achieved by genetic engineering. This review presents current knowledge and relevant results that aim to improve WUE in grapevines by biotechnology and genetic engineering. The expected benefits of these manipulations on WUE of grapevines under water stress conditions are modelled. There are two main possible approaches to achieve this goal: (i) to improve CO 2 diffusion to the sites of carboxylation without increasing stomatal conductance; and (ii) to improve the carboxylation efficiency of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The first goal could be attained by increasing mesophyll conductance to CO 2, which partly depends on aquaporins. The second approach could be achieved by replacing Rubisco from grapevine with Rubiscos from other C3 species with higher specificity for CO2. In summary, the physiological bases and future prospects for improving grape yield and WUE under drought are established.
195 citations
TL;DR: It is argued that the steady-state water potential of the epidermis in the intact leaf is controlled by the difference between the radiation-controlled rate of water vapor production in the leaf interior and the rate of transpiration, which provides a plausible explanation for the regulation of leaf and canopy transpiration by the radiation load.
Abstract: The terrestrial hydrological cycle is strongly influenced by transpiration—water loss through the stomatal pores of leaves. In this report we present studies showing that the energy content of radiation absorbed by the leaf influences stomatal control of transpiration. This observation is at odds with current concepts of how stomata sense and control transpiration, and we suggest an alternative model. Specifically, we argue that the steady-state water potential of the epidermis in the intact leaf is controlled by the difference between the radiation-controlled rate of water vapor production in the leaf interior and the rate of transpiration. Any difference between these two potentially large fluxes is made up by evaporation from (or condensation on) the epidermis, causing its water potential to pivot around this balance point. Previous work established that stomata in isolated epidermal strips respond by opening with increasing (and closing with decreasing) water potential. Thus, stomatal conductance and transpiration rate should increase when there is condensation on (and decrease when there is evaporation from) the epidermis, thus tending to maintain homeostasis of epidermal water potential. We use a model to show that such a mechanism would have control properties similar to those observed with leaves. This hypothesis provides a plausible explanation for the regulation of leaf and canopy transpiration by the radiation load and provides a unique framework for studies of the regulation of stomatal conductance by CO 2 and other factors.
TL;DR: It is demonstrated that constitutive traits controlling leaf water loss under well-watered conditions correlate with the terminal drought tolerance of pearl millet, which may lead to more water being available for grain filling under terminal drought.
Abstract: Pearl millet, a key staple crop of the semi-arid tropics, is mostly grown in water-limited conditions, and improving its performance depends on how genotypes manage limited water resources. This study investigates whether the control of water loss under non-limiting water conditions is involved in the terminal drought tolerance of pearl millet. Two pairs of tolerant x sensitive pearl millet genotypes, PRLT 2/89-33-H77/833-2 and 863B-P2-ICMB 841-P3, and near-isogenic lines (NILs), introgressed with a terminal drought tolerance quantitative trait locus (QTL) from the donor parent PRLT 2/89-33 into H77/833-2 (NILs-QTL), were tested. Upon exposure to water deficit, transpiration began to decline at lower fractions of transpirable soil water (FTSW) in tolerant than in sensitive genotypes, and NILs-QTL followed the pattern of the tolerant parents. The transpiration rate (Tr, in g water loss cm(-2) d(-1)) under well-watered conditions was lower in tolerant than in sensitive parental genotypes, and the Tr of NILs-QTL followed the pattern of the tolerant parents. In addition, Tr measured in detached leaves (g water loss cm(-2) h(-1)) from field-grown plants of the parental lines showed lower Tr values in tolerant parents. Defoliation led to an increase in Tr that was higher in sensitive than in tolerant genotypes. The differences in Tr between genotypes was not related to the stomatal density. These results demonstrate that constitutive traits controlling leaf water loss under well-watered conditions correlate with the terminal drought tolerance of pearl millet. Such traits may lead to more water being available for grain filling under terminal drought.
TL;DR: In this article, the authors focus on the deposition and fate of fine aerosols that are less than 2.5 micrometers in diameter and propose a new concept called hydraulic activation of stomata (HAS), which enables the efficient bidirectional transport of water and solutes between the leaf interior and leaf surface.
Abstract: Aerosols have always been part of the atmosphere, and plant surfaces are a major aerosol sink. Given the nutrient content of aerosols and the natural stability of aerosol concentrations over evolutionary time, plants may have developed adaptations to aerosol input. Although little is known about such adaptations, leaf surface micro-roughness appears to play a key role. This review focuses on the deposition and fate of fine aerosols that are less than 2.5 μm in diameter. Most of these aerosols are hygroscopic, and they are often deliquescent (liquid) on transpiring leaves. Such concentrated solutions may be taken up by both the cuticle and stomata, contradicting previous concepts. The establishment of a continuous liquid water connection along stomatal walls affects individual stomata and is a new concept called “hydraulic activation of stomata” (HAS). HAS enables the efficient bidirectional transport of water and solutes between the leaf interior and leaf surface and makes stomatal transpiration partly in...
TL;DR: Since the plants subjected to mild water and salt stresses showed a rapid and almost complete recovery, these physiological alterations could represent a set of adaptive mechanisms employed by J. curcas to cope with these stressful conditions.
TL;DR: Data for RD20, a stress-inducible Arabidopsis gene that belongs to the caleosin family, shows that RD20 is expressed in leaves, guard cells and flowers, but not in root or in mature seeds, and supports a role forRD20 in drought tolerance through stomatal control under water deficit conditions.
Abstract: Plants overcome water deficit conditions by combining molecular, biochemical and morphological changes. At the molecular level, many stress-responsive genes have been isolated, but knowledge of their physiological functions remains fragmentary. Here, we report data for RD20, a stress-inducible Arabidopsis gene that belongs to the caleosin family. As for other caleosins, we showed that RD20 localized to oil bodies. Although caleosins are thought to play a role in the degradation of lipids during seed germination, induction of RD20 by dehydration, salt stress and ABA suggests that RD20 might be involved in processes other than germination. Using plants carrying the promoter RD20::uidA construct, we show that RD20 is expressed in leaves, guard cells and flowers, but not in root or in mature seeds. Water deficit triggers a transient increase in RD20 expression in leaves that appeared predominantly dependent on ABA signaling. To assess the biological significance of these data, a functional analysis using rd20 knock-out and overexpressing complemented lines cultivated either in standard or in water deficit conditions was performed. The rd20 knock-out plants present a higher transpiration rate that correlates with enhanced stomatal opening and a reduced tolerance to drought as compared with the wild type. These results support a role for RD20 in drought tolerance through stomatal control under water deficit conditions.
TL;DR: In this article, the authors used a modified and specially calibrated soil respiration chamber to directly measure E on a weekly basis at 14 permanently installed soil collars across the range of soil surface conditions.
TL;DR: Mixed eucalypt–acacia plantations may be used in water-limited environments to produce a given amount of wood with less water than eucallypt monocultures, and because mixtures can be more productive and use more water per unit land area (but use it more efficiently), they could be utilized in recharge zones where rising water tables and salinity result from the replacement of vegetation that uses higher quantities of water.
TL;DR: The results indicated that AM symbiosis protect maize plants against low temperature stress through improving the water status and photosynthetic capacity.
Abstract: The effect of arbuscular mycorrhizal (AM) fungus, Glomus etunicatum, on growth, water status, chlorophyll concentration and photosynthesis in maize (Zea mays L.) plants was investigated in pot culture under low temperature stress. The maize plants were placed in a sand and soil mixture at 25°C for 7 weeks, and then subjected to 5°C, 15°C and 25°C for 1 week. Low temperature stress decreased AM root colonization. AM symbiosis stimulated plant growth and had higher root dry weight at all temperature treatments. Mycorrhizal plants had better water status than corresponding non-mycorrhizal plants, and significant differences were found in water conservation (WC) and water use efficiency (WUE) regardless of temperature treatments. AM colonization increased the concentrations of chlorophyll a, chlorophyll b and chlorophyll a + b. The maximal fluorescence (Fm), maximum quantum efficiency of PSII primary photochemistry (Fv/Fm) and potential photochemical efficiency (Fv/Fo) were higher, but primary fluorescence (Fo) was lower in AM plants compared with non-AM plants. AM inoculation notably increased net photosynthetic rate (Pn) and transpiration rate (E) of maize plants. Mycorrhizal plants had higher stomatal conductance (gs) than non-mycorrhizal plants with significant difference only at 5°C. Intercellular CO2 concentration (Ci) was lower in mycorrhizal than that in non-mycorrhizal plants, especially under low temperature stress. The results indicated that AM symbiosis protect maize plants against low temperature stress through improving the water status and photosynthetic capacity.
TL;DR: The population from the uncontaminated site (Zijinshan) had a remarkable ability to accumulate Cd in shoots to concentrations well in excess of 100 microM in the hydroponic experiment, similar to the population from contaminated site, suggesting that Cd accumulation is a constitutive trait of P. americana.
TL;DR: In this article, the authors investigated four years of transpiration estimates from sap flux, interception-evaporation estimates from precipitation and throughfall gauges, modeled soil evaporation and drainage estimates, and eddy covariance data in a mature oak-hickory forest in North Carolina, USA.
Abstract: Although drought in temperate deciduous forests decreases transpiration rates of many species, stand-level transpiration and total evapotranspiration is often reported to exhibit only minor interannual variability with precipitation. This apparent contradiction was investigated using four years of transpiration estimates from sap flux, interception–evaporation estimates from precipitation and throughfall gauges, modeled soil evaporation and drainage estimates, and eddy covariance data in a mature oak-hickory forest in North Carolina, USA. The study period included one severe drought year and one year of well above-average precipitation. Normalized for atmospheric conditions, transpiration rates of some species were lower in drought than in wet periods whereas others did not respond to drought. However, atmospheric conditions during drought periods are unlike conditions during typical growing season periods. The rainy days that are required to maintain drought-free periods are characterized by low atmospheric vapor pressure deficit, leading to very low transpiration. In contrast, days with low air vapor pressure deficit were practically absent during drought and moderate levels of transpiration were maintained throughout despite the drying soil. Thus, integrated over the growing season, canopy transpiration was not reduced by drought. In addition, high vapor pressure deficit during drought periods sustained appreciable soil evaporation rates. As a result, despite the large interannual variation in precipitation (ranging from 934 to 1346 mm), annual evapotranspiration varied little (610–668 mm), increasing only slightly with precipitation, due to increased canopy rainfall interception. Because forest evapotranspiration shows only modest changes with annual precipitation, lower precipitation translates to decreased replenishment of groundwater and outflow, and thus the supply of water to downstream ecosystems and water bodies.
TL;DR: The study found that the deleterious effects of alkali stress were more severe than those of salt stress, indicating that alfalfa was relatively sensitive to both stresses during seed germination and early seedling growth stages.
Abstract: Alfalfa (Medicago sativa L.) is one of the most important forage crops and has high protein and highly digestible fibre contents. It can be cultivated in moderate salt-alkaline soils and has been widely cultivated as an economic crop worldwide. We quantified the effects of salt (1:1 molar ratio of NaCl to Na2SO4, pH 7.01–7.05) and alkali (1:1 molar ratio of NaHCO3 to Na2CO3, pH 9.80–10.11) stresses on germination, growth, photosynthesis and ion accumulation in alfalfa. The results showed that both stresses significantly reduced germination and radicle elongation, indicating that alfalfa was relatively sensitive to both stresses during seed germination and early seedling growth stages. The relative growth rate, water content, chlorophyll content, intercellular CO2 concentration, stomatal conductance, net photosynthetic rate (PN) and transpiration rate decreased slightly with increasing salinity under salt stress, but were markedly reduced under alkali stress. Conversely, water use efficiency incre...
TL;DR: A comprehensive whole-tree model is developed that enables simulation of the stem diameter variations driven by both the water and sugar transport and is able to simulate several physiological variables which are relatively difficult to measure:phloem turgor, phloem osmotic pressure, and Münch's counterflow.
Abstract: In trees, water and sugars are transported by xylem and phloem conduits which are hydraulically linked. A simultaneous study of both flows is interesting, since they concurrently influence important processes such as stomatal regulation and growth. A few mathematical models have already been developed to investigate the influence of both hydraulically coupled flows. However, none of these models has so far been tested using real measured field data. In the present study, a comprehensive whole-tree model is developed that enables simulation of the stem diameter variations driven by both the water and sugar transport. Stem diameter variations are calculated as volume changes of both the xylem and the phloem tissue. These volume changes are dependent on: (i) water transport according to the cohesion-tension theory; (ii) sugar transport according to the Munch hypothesis; (iii) loading and unloading of sugars; and (iv) irreversible turgor-driven growth. The model considers three main compartments (crown, stem, and roots) and is verified by comparison with actual measured stem diameter variations and xylem sap flow rates. These measurements were performed on a young oak (Quercus robur L.) tree in controlled conditions and on an adult beech (Fagus sylvatica L.) tree in a natural forest. A good agreement was found between simulated and measured data. Hence, the model seemed to be a realistic representation of the processes observed in reality. Furthermore, the model is able to simulate several physiological variables which are relatively difficult to measure: phloem turgor, phloem osmotic pressure, and Munch's counterflow. Simulation of these variables revealed daily dynamics in their behaviour which were mainly induced by transpiration. Some of these dynamics are experimentally confirmed in the literature, while others are not.
TL;DR: Hydraulic redistribution mitigated the effects of soil drying on understory and stand evapotranspiration and had important implications for net primary productivity by maintaining this whole ecosystem as a carbon sink.
Abstract: Summary • Hydraulic redistribution (HR) of water via roots from moist to drier portions of the soil occurs in many ecosystems, potentially influencing both water use and carbon assimilation. • By measuring soil water content, sap flow and eddy covariance, we investigated the temporal variability of HR in a loblolly pine (Pinus taeda) plantation during months of normal and below-normal precipitation, and examined its effects on tree transpiration, ecosystem water use and carbon exchange. • The occurrence of HR was explained by courses of reverse flow through roots. As the drought progressed, HR maintained soil moisture above 0.15 cm 3 cm )3 and increased transpiration by 30–50%. HR accounted for 15–25% of measured total site water depletion seasonally, peaking at 1.05 mm d )1 . The understory species depended on water redistributed by the deep-rooted overstory pine trees for their early summer water supply. Modeling carbon flux showed that in the absence of HR, gross ecosystem productivity and net ecosystem exchange could be reduced by 750 and 400 g C m )2 yr )1 , respectively.
TL;DR: The results suggest that deep-rooted plants are important drivers of water cycling in dry ecosystems and that HR can significantly influence landscape hydrology.
Abstract: Deep water uptake and hydraulic redistribution (HR) are important processes in many forests, savannas and shrublands. We investigated HR in a semi-arid woodland above a unique cave system in central Texas to understand how deep root systems facilitate HR. Sap flow was measured in 9 trunks, 47 shallow roots and 12 deep roots of Quercus, Bumelia and Prosopis trees over 12 months. HR was extensive and continuous, involving every tree and 83% of roots, with the total daily volume of HR over a 1 month period estimated to be approximately 22% of daily transpiration. During drought, deep roots at 20 m depth redistributed water to shallow roots (hydraulic lift), while after rain, shallow roots at 0-0.5 m depth redistributed water among other shallow roots (lateral HR). The main driver of HR appeared to be patchy, dry soil near the surface, although water may also have been redistributed to mid-level depths via deeper lateral roots. Deep roots contributed up to five times more water to transpiration and HR than shallow roots during drought but dramatically reduced their contribution after rain. Our results suggest that deep-rooted plants are important drivers of water cycling in dry ecosystems and that HR can significantly influence landscape hydrology.
TL;DR: Genotypic variation in g(m) was found between genotypes, and was correlated with photosynthetic rate, suggesting g( m) has unexplored potential to provide TE improvement within crop breeding programmes.
Abstract: Leaf internal, or mesophyll, conductance to CO2 (gm )i s a significant and variable limitation of photosynthesis that also affects leaf transpiration efficiency (TE). Genotypic variation in gm and the effect of gm on TE were assessed in six barley genotypes (four Hordeum vulgare and two H. bulbosum). Significant variation in gm was found between genotypes, and was correlated with photosynthetic rate. The genotype with the highest gm also had the highest TE and the lowest carbon isotope discrimination as recorded in leaf tissue (Dp). These results suggest gm has unexplored potential to provide TE improvement within crop breeding programmes.
TL;DR: It is concluded that leaf size is conservative for survival over relatively rare periods of hot dry conditions with low wind speeds, and small leaf dimensions confer a capacity for high transpiration when evaporative demand is low and water is abundant.
Abstract: Summary 1. Small leaves of species endemic to Mediterranean-type climate areas have been associated with both low rainfall and nutrient availability, but the physiological reasons for this association remain unknown. 2. We postulated that small leaves have thin boundary layers that facilitate transpiration in winter and sensible heat loss in summer. High transpiration rates when water is available may facilitate nutrient acquisition in winter, whereas efficient sensible heat loss reduces the requirement for transpirational leaf cooling in summer. 3. The consequences of varying leaf sizes for water and heat loss in Cape Proteaceae were examined at two scales. At the leaf level, gas exchange and thermoregulatory capacities of 15 Proteaceae species with varying leaf size were assessed under controlled conditions using phylogenetically independent contrasts. At an environmental level, leaf attributes of Proteaceae occurring in the winter-rainfall area of the Cape Floristic Region were correlated with climatic environments derived from distribution data for each species. 4. Leaf temperature was positively correlated with leaf size when wind speed was negligible. However, transpiration decreased significantly with increasing leaf size when measured on individual leaves, detached branches and when expressed on a per stoma basis. 5. From multiple stepwise regression analysis of climatic variables obtained from distribution data, leaf size was negatively correlated with A-Pan evaporation, mean annual temperatures and water stress in January. We conclude that leaf size is conservative for survival over relatively rare periods of hot dry conditions with low wind speeds. 6. Narrow leaves enable plants to shed heat through sensible heat loss during summer droughts, without the need for transpirational cooling. Additionally, small leaf dimensions confer a capacity for high transpiration when evaporative demand is low and water is abundant (i.e. winter). This may be a particularly important strategy for driving nutrient mass-flow to the roots of plants that take up most of their nutrients in the wet winter ⁄ spring months from nutrient-poor soils.
TL;DR: In this paper, the authors used heat field deformation technique (HFD) for measuring sap flow in several forest species and sites across Europe, and were able to provide evidence on different types of hydraulic redistribution (VHR), horizontal hydraulic redistribution, foliar uptake (FU), and tissue dehydration (TD).
Abstract: The upward movement of water due to transpiration stops when soil water potential (Ψs) drops below leaf water potential (Ψ L ). Under these circumstances, water can move in any direction in the plant-soil continuum through the passive conduits of roots and stems towards the lowest Ψ s . This is generally termed as hydraulic redistribution (HR), but the positioning and orientation of the driving water potential gradient may vary. Any experimental method that can measure bi-directional and low flows in the sapwood of roots and stems will be suitable to detect HR. Using one approach for measuring sap flow (the heat field deformation technique, HFD) in several forest species and sites across Europe, we were able to provide evidence on different types of HR: vertical hydraulic redistribution (VHR), horizontal hydraulic redistribution (HHR), foliar uptake (FU) and tissue dehydration (TD). VHR is the vertical water movement through roots in response to water potential differences between deep and topsoil, either hydraulic lift or hydraulic descent. HHR is the lateral water movement through roots in response to horizontal water potential gradients, namely under localised irrigation. FU is the water movement from crown to soil through stems when the crown is wetted by foggy weather. TD is the downward movement of water in stems or roots from above-ground tree tissues to soil under prolonged drought or frost. Results from direct sap flow measurements indicated the vectoral and widespread nature of HR, a phenomenon of paramount importance for overall physiology and ecohydrology.
TL;DR: Gas exchange responses to static and variable light were tested in snap bean and oaks, suggesting that O(3)-induced stomatal sluggishness is a common trait among different plant physiognomic classes.
TL;DR: In this paper, the relationship between Ca uptake by tree fine roots and the pattern of δ44Ca enrichment with soil depth was modeled for two Ca pools: the forest floor (litter) and the underlying (upper B) mineral soil.
TL;DR: The present opinion paper discusses the significance of the variable water transport capacity (hydraulic conductance) of roots during development and in response to environmental stimuli and indicates how the dynamics of root hydraulics contributes to many integrated plant nutritional and growth functions.
Abstract: Roots are the primary sites of water uptake by plants. Roots also sense most of the physico-chemical parameters of the soil, perceive signals from the shoots, and adjust their growth and water transport properties accordingly. The present opinion paper discusses the significance of the variable water transport capacity (hydraulic conductance) of roots during development and in response to environmental stimuli. It is shown that root hydraulics determines water uptake intensities but also water potential gradients within the plant. It is indicated how the dynamics of root hydraulics contributes to many integrated plant nutritional and growth functions. For instance, the heterogeneity of soil water and nutrient availability and the heterogeneity of root hydraulic properties feed each other and play critical roles in root transport functions. Another important aspect is the integration of root hydraulics within the mutual interactions of roots and shoots, for co-ordinated growth and water-saving responses to drought.